As President Obama prepared to unveil his plan to overhaul the nation’s immigration system Tuesday, advocates for immigrants in Massachusetts and nationwide mobilized for what they say is their best chance in almost three decades to secure a path to US citizenship for 11 million illegal immigrants in the United States.

Advocates say Obama’s ­recent victory and Republican attempts to appease Latino voters who flexed their political muscle last year could propel Congress to pass legislation that has failed repeatedly, even as the number of illegal immigrants climbed to the highest levels in US history.

“I think it’s going to happen this year,” said Eva A. Millona, executive director of the Massachusetts Immigrant and Refugee Advocacy Coalition, which is among the groups pushing for citizenship and other changes. “The blueprint is out there. The expectation is there.”

Obama is to reveal his plan for immigration Tuesday in a speech at Del Sol High School in Las Vegas, in the home state of Senate majority leader Harry Reid,
where the Latino population has ballooned in the last decade.

The president’s speech comes one day after a bipartisan group of eight senators, including New York Democrat Charles Schumer and Republican John McCain of Arizona, released their own immigration proposal in Washington, calling it a “tough, fair, and practical road map” that would let illegal immigrants pay a fine and back taxes and apply for legal residency, and someday, US citizenship. The plan would also make it easier for farm workers and highly educated immigrants to remain in the country. Serious criminals would still be subject to deportation.

The senators’ plan also would beef up immigration enforce­ment in the United States and punish businesses that hire illegal workers with “stiff fines and criminal penalties.”

“We will ensure that this is a successful permanent reform to our immigration system that will not need to be revisited,” the senators said in a statement released Monday.

Details of the president’s proposal were sparse in ­advance of his speech. But it is expected to be similarly sweeping at fixing what the White House called “our broken immi­gration system so it is fair and helps grow our middle class and it ensures everyone is playing by the same rules.”

Critics of the Senate group’s plan said they have heard promises of tough and lasting changes before, such as in the bipartisan legislation known as the Immigration Reform and Control Act that Ronald Reagan signed in 1986. The law legalized nearly 3 million illegal immi­grants and promised to ­increase enforcement, making it a crime for employers to knowingly hire illegal immigrants. But enforcement proved to be weak, allowing the illegal immigrant population to soar to 12 million nationwide, though the numbers have since declined, along with the economy.

“Nobody’s going to want to repeat that mistake that obviously didn’t fix the problem,” said Jessica Vaughan, director of policy studies for the Center for Immigration Studies, a group in Washington that ­favors limits on immigration.

Vaughan, who lives in Massa­chusetts, said she doubted a massive package such as the senators’ proposal would pass because of ongoing opposition to illegal immigration, and she pointed out that bipartisan efforts have failed before, includ­ing one led by President Bush in 2007. She said that Congress would be more likely to approve less ambitious legislation, such as a bill that would let the undocumented children of illegal immigrants stay in the United States.

“On the immigration issue, bipartisan doesn’t mean much, because this issue does not ­divide along traditional partisan lines,” she said.

Other groups, such as the Federation for American Immigration Reform, slammed the senators’ proposal Monday and vowed to fight it.

“We expect that once the American public learns of the details of this proposal and comes to recognize that it will do nothing to fix the problems of our broken immigration system, it will meet with the same overwhelmingly negative ­response that it ­received in 2007,” said the group’s president, Dan Stein.

Others were cautiously optimistic, particularly grass-roots immigration groups who have been disappointed by the Obama administration’s tough approach to illegal immigration in the past.

In Boston and nationwide, the walls of immigration courts are still papered with the names of immigrants from ­Brazil, China, and El Salvador who face deportation every day, and last year federal immigration officials deported 409,849 immigrants, including more than 184,000 people who had no criminal records.

Hours before the senators unveiled their proposal Monday, Patricia Montes and several other advocates stood in the frigid cold before US Immigration and Customs Enforcement’s offices in Burlington, hoping to forestall deportation of a 36-year-old mother of three from Guatemala.

“We are optimistic, but we know that we have to do a lot of work,” said Montes, executive director of Centro Presente, a statewide group based in Somerville that advocates for immigrants. “There are too many people around the US confronting the same situation.”

President Obama’s speech Tuesday in some ways circles back to his first year in office. In his 2008 campaign, the president promised to tackle immigration reform in his first year in office, but the issue faded amid economic problems after the stock market crash. States such as Arizona and Georgia passed their own laws restricting immigration, and others, including Massachusetts, held passionate debates.

But analysts say 2013 could be ripe for the most significant immigration overhaul since 1986. The economy is improving, companies and agriculture need workers, and, after Mitt Romney’s bruising loss to Obama last year, Republicans feel compelled to reach out to Latino voters.

“I think that this year we’re in the best position to pass a bill,” said Roberto Gonzales, a sociologist and a professor at the University of Chicago in ­Illinois, where the governor just signed a measure to give driver’s licenses to illegal immigrants, a rarity in the United States. “Certainly it’s the best chance we have.”

Though many advocates are hopeful that an immigration overhaul will pass this year, they say working out the ­details could take months, if not longer. Will lawmakers pass a massive immigration package or several small pieces? Will immi­grants have to pay a fine for being here illegally, and if so, how much?

“Things have changed,” said Professor Frank D. Bean, director of the Center for Research on Immigration, Population, and Public Policy at the University of California, Irvine.

“But there’s still a lot of things that have to happen,’’ he said. “There’s a lot of issues ­involved and a lot of political nuances and so on.”

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